Control system with gas discharge tube



Oct. 21, 1947. CADE 2,429,451

CONTROL SYSTEM WITH GAS DISCHARGE TUBE Filed Nov. 16, 1944 2 Sheets-Sheet l aA'rA'er/mv Io/f l2 F//P//V0 1% ;.-1---- O g F r/M:

Oct. 21, 1947. P. J. CADE ,4

CONTROL SYSTEM WITH GAS DISCHARGE TUBE Filed Nov. 16, 1944 2 sheds-sheet? be made more positive relatively to Patented Oct. 21, 1947 2,429,451 CONTROL SYSTEM WITH GAS DISCHARGE TUBE Phillip J. Oadc, Cambridge, lltotolwiich Incorporated,

Mala, auignor to Cambridge, Mala,

a corporation of Massachusetts. Application November 18, 1944, Serial No. 583,731 14 Claims. (CL 122-504) This invention relates to electronic devices and to a method for operating such devices, and more particularly to industrial control systems or this type which operate with gas-filled electron disseveral detecting impedances, and which furnish ample current for the safe operation or a load in the output circuit of a gas discharge tube; to provide devices of this type which operate in response to several detecting or control impedances which are completely isolated from each other; to provide circuits of this type which can be safely operated under the control of phototubes including gas-filled phototubes; to provide a method for operating gaseous or glow discharge tubes with a very high degree of sensitivity due to much-reduced starting current; and generally to provide circuits containing a gas discharge tube as a control element, and a method for operating such circuits, which are highly sensitive, economical in operation and yet simple and reliable.

It is well known that in order to initiate current flow between the main electrodes of a gas discharge tube, a voltage and a current flow of certain values must exist between cathode and starting electrode. If either one of these values prevails without the other, starting ionization suflicient to initiate the main discharge will not be provided.

It has heretofore been presumed that the flow (this concept being herein used in the conventional sense, from anode to cathode, opposite to the electron flow) of starting current must proceed from the starting electrode to the cathode, or in other words that in order to start the gas discharge tube, the starting electrode must be more positive than the cathode, so that, in order to initiate breakdown and conductivity'of the tube, the potential of the starting electrode must the cathode.

I have found that all three-element coldcathode gas-filled tubes commercially available to me at the present time can be rendered conductive while the starting or auxiliary electrode is more negative than the cathode, so long as the necessary starting current and voltage values are present. With this mode of operation, the starting electrode operates so to speak as a starting cathode, with they cathode acting as an anode, whereas, as soon as the starting ionization is reached, the cathode assumes its regular function of providing for current flow thereto from the main anode. Circuits incorporating this principle of starting a gas-discharge tube are especially advantageous because the ionization current required for causing transition from starting to main discharge is with this mode of operation much less, sometimes as low as one hundredth, of that necessary when the starting current flows to the cathode from a more positive starting electrode. Therefore, 'a tube operated in this manner, namely by rendering, for starting the tube, the auxiliary electrode potential more negative relatively to the cathode, is much more sensitive as compared to its conventional use with an auxiliary electrode that is, during the starting period, more positive relatively to the cathode. I

These and other objects, aspects and features of the present invention will be more fully apparent from the following description of several practical embodiments illustrating the genus of the invention. This description refers to a drawing in which Figs. 1 and 3 are circuit diagrams illustrating the basic principle of the present circuit, for operation with direct current and alternating current, respectively;

Figs. 2 and 4 are diagrams illustrating the operation of circuits according to Figs. 1 and 3 respectively;

Fig. 5 is the circuit diagram of a burner control installation incorporating a circuit according to the invention; and

Fig. 6 is a diagram similar to Figs. 2 and 4, illustrating operation with starting current whose phase is shifted relatively to the anode voltage.

In Fig. 1, letters A and B indicate two terminals or wires supplied with direct current. A potential apportioning device such as potentiometer R. is connected across wires A and B. A gas-filled electron discharge tube K, with anode a, cathode k, and starting electrode 1 is connected between terminal A and the tap b of potentiometer B. An operator load ZI, such as the magnet of a relay switch is inserted in the output circuit of tube K. A normally closed restoring switch, such as push-button switch s is provided in the output circuit of tube K, for example between cathode k and adjustable tap b.

The starter electrode 1 is connected, in a starting circuit N, to an adjustable tap d of potentiometer R, which tap d provides a potential which is lower than that derived from tap b supplying cathode k. Between electrode 1 and tap d is connected a control or detecting impedance Z2, indicated in Fig. l as an adjustable resistor. In series with the detecting impedance may beconnected a limiting resistance RI. A bypass capacitor C may be connected between electrode 2' and wire B.

This arrangement operates as follows.

Under operating conditions with ZI deenergized, which condition may be considered normal, detecting impedance Z2 is high enough to limit the current which may flow between electrode i and cathode is to a value which is below that able to provide ionization suflicient to cause breakdown of tube K and conductivity between cathode k and anode a. The voltage between electrode 1' and cathode k, with 2' having a potential more negative than that of it due to the above-mentioned arrangement of taps b and d,

- may or may not be that required for causing the minimum ionization necessary for starting the tube.

If the impedance Z2 now decreases sufliciently to permit increased flow in circuit and if this increased current reaches the starting ionization value, the space between i and k will be sufficiently ionized to initiate gaseous discharge between the main electrodes of tube K. The voltage between i and k may or may not increase when the current flowing between i and it increases, but at any rate the potential of i will be more negative than that of it. As well known, tube K will remain conductive, regardless of the condition of auxiliary electrode 2'. In order to restore tube K to nonconducting condition, restoring switch s has to be opened in order to interrupt the output circuit of tube K. If, upon reclosing the restoring switch 3, the starting circuit N is still in starting condition, tube K will again become conductive.

The above-described operation is further explained in diagram Fig. 2 which, considering the legends applied to its various curves, will now be self explanatory. Attention is especially called to the starter anode current which increases in negative direction, that is in the conventional flow direction from cathode k to electrode 1', until the tube breaks down, whereupon current begins to flow in the usual direction from anode a to cathode k. It will be understood that in a diagram of this type, the transient configurations can be reproduced only with an accuracy sufficient to indicate the qualitative character of the operation.

Fig. 3 illustrates an arrangement quite similar to that of Fig. 1, but for alternating current operation. In this figure, D and F are supply terminals or wires connected to an alternating current source. A transformer L is with its primary Lp connected across wires D and F. The gas-discharge tube K, with operator load Zl in its output circuit, is connected between the high potential terminal e of transformer L and wire D. The starting electrode 2' is connected to the low potential terminal f of transformer secondary Ls, through a detecting impedance Z2 and a limiting resistor RI. This figure indicates the possibility of varying impedance Z2 b means of a starting switch S bridging Z2 and for example normally open. Impedance Z2 may also be a phototube with its anode connected to i and its cathode to RI, as in the embodiment to be described with reference to Fig. 5. A bypass capacitor C is preferably connected between electrode 1' and wire F.

The windings of transformer L are so arranged that the voltages in primary Lp and secondary Ls are out of phase, so that electrode 2 will be negative when wire D and anode a of tube K are positive.

The arrangement according to Fig. 3 operates as follows.

Again considering first the condition when tube K is nonconductive, the current which may flow between auxiliary electrode 1 and cathode is is in-- sumcient to ionize tube K sufilciently for breakdown and Zl is deenergized.

If impedance Z2 is now decreased, for example by closing switch S, the negative peak potential reached by auxiliary electrode 1' will, during the half cycle in question, reach a value which, toether with a simultaneous positive potential of anode a, causes current flow from k to i suificient to ionize the tube for breaking it down and start ing the main discharge between it and a. It will be evident that impedance Z2 together with switch S could be replaced by a, continuously variable detecting impedance as shown in Fig. 1.

The resistor RI has the purpose of limiting the starting current between is and i to harmless values, if the detecting or starting impedance Z2 should assume a very low value.

The above-described operation will be better understood with the aid of diagram Fig. 4 which is analogous to that of Fig. 2 and which indicates clearly that with increased negative potential of electrode 2', and increased current between R: and i the tube becomes ionized between i and k, causing it to break down for gaseous discharge between it and a.

Fig. 5 illustrates the application of a circuit according to Fig. 3 to a flame supervising installation which is somewhat similar to that disclosed in Patent No. 2,358,432 to William F. Wolfner II, dated September 19, 1944.

In this figure D and F are again the terminal wires of an alternating current source. The primary Lip of a starter transformer Ll is connected between wires D and F. One terminal of the transformer secondary Lls is connected to a wire m which may lead to one probe terminal, in the present instance the grounded boiler of a heating installation which will be described in detail hereinbelow. The grounded connection m may be joined to supply wire F. The other terminal of the transformer secondary Lls is connected through a, resistor R2 to one terminal of the secondary L21) of a second starter transformer L2. The other terminal of the transformer primary L2 is connected through a capacitor C2 to a second probe terminal n which, as indicated in Fig. 5, may be connected to a water level probe 1). One terminal of transformer secondary L2s may be connected to the grounded supply wire F. The other terminal of trans former secondary Us is connected to the cathode kp of a phototube P.

A gas-discharge tube K is connected across terminal wires D and F, through relay magnet M which may operate a switch sl that is held open while M is energized. Magnet M is in the usual manner bridged by a sustaining capacitor C3 in series with a resistor R3.

of tube K is connected to the anode up of photo- The starter electrode i tube P through a limiting resistor R. A bypass capacitor C4 is connected between electrode 1 and terminal wire F.

The gap G formed between ground and probe p, and phototube P constitute a first and second variable detecting impedance. connected in a first and second starting circuit NI and N2, respectively.

As indicated above, probe p is arranged to supervise the level of the water in a boiler schematically indicated at l 0! Fig. 5. A normal water level I I connects terminal m of transformer secondary Lie to transformer primary L2 7, in circuit Ground-4 0-m-L l s --R2-L2p The boiler l0 may be equipped with a burner l5, for example a gas burner supplied through a valve l8 controlled by an operator I! which is energized through switch sl, controlled by relay magnet M as above described. The phototube P observes the flame 20 through a suitably arranged supervising tube 2| directed at flame 20.

The arrangement according to Fig. 5 operates as follows.

Under normal operating conditions, valve l6 must be open, with switch sl open and magnet M energized. Transformers Li and L2, connected in circuits Ni and N2 including the closed probe connection from m to n through G apply the proper polarizing voltage to phototube P. It will be observed that, contrary toknown arrangements as for example that described in the above-mentioned patent to William F. Woliner, the phototube anode ap is connected to the starter electrode 1 of gas tube K. This arrangement conforms with that of the transformers LI and L2 which, as described with reference to Fig. 3, are so connected that electrode i is negative during the half cycle when anode a of tube K is positive. The starting current flows accordingly in circuit F-k-L-Rd-ap-kwLZ-Ll-D, with k more positive than i and up more positive than kp. With flame illuminating phototube P, the latter is sufflciently conductive to supply to tube K the necessary starting current. Under these operating conditions, tube K is therefore conductive and M energized as above presumed.

If the water level should fall below probe p the connection between transformers LI and L2 is interrupted, the voltage supplied to phototube P becomes insuflicient for its operation, the current through electrode i falls below the minimum starting value, and tube K becomes nonconductive.

If the flame 20 should become extinguished, the conductivity of phototube P decreases so that sufficient starting current is not supplied to starter electrode 1 and cathode k, as above explained.

It will be evident that either abnormal water level or extinction of flame 20 causes tube K to become nonconductive and mag-net M deenergized, closing switch sl. This may cause ringing of alarm bell 30 and closing of valve it or any other appropriate chain of operations, for example including the starting of a feedwater pump. Upon restoration of normal operating conditions either by hand or automatically with well-known means, that is when the water level again reaches probe p and flame 20 is again burning, the voltage and current values necessary for starting tube K will again be applied to starter electrode 2 and the system is again in normal operating condition as indicated in Fig. 5.

If a high vacuum phototube is used, there exists little danger that the voltage surge, which occurs when the tube K breaks down and the starter electrode suddenly assumes a positive potential, will injure the phototube. However, it may be advisable to use limiting resistors R2 and R4, or at least one of these, in order to limit the phototube current to a safe value, especially if the phototube is of the gas-filled type. In the latter instance the phototube might become ionized when the starter electrode is drawn positive by the discharge right after starting. I

In order to assure safe operation of relay magnet M, it may be advisable to use, in accordance with one of the aspects of the invention, the'following arrangement of the starter electrode circuit.

A capacitor C2 is inserted in the circuit connecting the two transformers, which causes the alternating current supplied through starter electrode i to be somewhat advanced in phase as compared to the voltage supply of anode a. As illustrated in Fig. 6, this provides starting conditions before the main wave reaches its peak value, so that magnet M is supplied with current during a considerable period of the positive half cycle.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope oi! the appended claims.

I claim:

1. The method oi? operating a gaseous discharge tube having anode, cathode and starter electrode of the type wherein the starter electrode is normally used for efiecting a starting discharge between said starter electrode and said cathode, characterized by applying to said electrode, for starting the tube, a potential that is negative with regard to that of said cathode and current sufilcient to ionize a path between said electrode and said cathode while they act as starter cathode and anode, respectively, but not sufllcient to ionize a path between said electrode and said anode, whereupon the main current path between said anode and said cathode becomes established with current flowing in the substantially fully ionized gas between said anode and said cathode.

2. The method of operating a gaseous discharge tube having anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, characterized by applying to said electrode while the tube is in normal nonconductive condition, a potential that is more negative than that of the cathode and, for starting the tube, by applying to said electrode a negatively increased potential and current suiiicient to ionize a path between said electrode and said cathode while they act as starter cathode and anode, respectively, but not suiiicient to ionize a path between said electrode and said anode, whereupon the main current path between said anode and said cathode becomes established with current flowing in the substantially fully ionized gas between said anode and said cathode.

3. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying an operating voltage to said anode and said cathode, starting circuit means for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a. current path through said electrode and said cathode, and means for causing said starting circuit means to carry current flowin from said cathode to said electrode and adapted to ionize gas in the tube sufficiently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode.

4. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for efifecting a starting discharge between said starter electrode and said cathode, comprising means for applying an operating voltage to said anode and said cathode, starting circuit means for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, and means for negatively increasing said starter electrode potential and causing said starting circuit means to carry current flowing from said cathode to said electrode and adapted to ionize gas in the tube suificiently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode.

5. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying an operating voltage to said anode and said cathode, and starting circuit means including means for applying to said electrode a potential that is negative with respect to the potential of said cathode and a phototube whose anode means is connected to said electrode and which provides a current path through said electrode and said cathode, said phototube when illuminated to a predetermined degree passing an amount of current through said path and from said cathode to said electrode which in the presence of said negative potential ionizes gas in said discharge tube sufliciently between said cathode and said electrode to cause the gaseous discharge tube to become conductive with current flowing from said anode to said cathode.

6. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying a unidirectional operating voltage to said anode and said cathode, and starting circuit means including voltage apportioning means and a variable detecting impedance for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, said detecting impedance when reduced to a predetermined value negatively increasing said starter electrode potential and causing said starting circuit means to carry current flowing 8 from said cathode to said electrode in sufllcient quantity in the presence of said negatively increased potential to ionize gas in said tube sufflciently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anodeto said cathode.

'7. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying an alternating operating voltage to said anode and said cathode, .and starting circuit means including transformer means and a variable detecting impedance for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, said detecting impedance when reduced to a predetermined value negatively increasing said starter electrode potential and causing said starting circuit means to carry current flowing from said cathode to said electrode in suflicient quantity in the presence of said negatively increased potential to ionize gas in said tube sufllciently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode.

8. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising connecting means for applying a unidirectional operating voltage to said anode and said cathode, starting circuit means including voltage apportioning means and a variable detecting impedance for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a, current path through said electrode and said cathode, and normally closed circuit interrupting means in said connecting means, said detecting impedance when reduced to a predetermined value negatively increasing said starter electrode potential and causing said starting circuit means to carry current flowing from said cathode to said electrode in suflicient quantity in the presence of said negatively increased potential to ionize gas in said tube sufficiently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode while said interrupting means remains closed.

9. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying an alternating operating voltage to said anode and said cathode, and starting circuit means including transformer means for applying to said electrode a potential that is negative with respect to the potential of said cathode and a phototube whose anode means is connected to said electrode and which provides a current path through said electrode and said cathode, said phototube when illuminated to a predetermined degree passing an amount of current through said path and from said cathode to said electrode which in the pres- ,ence of said negative potential ionizes gas in said discharge tube sufllciently between said cathode and said electrode to cause the gaseous discharge tube to become conductive with current flowing from said anode to said cathode.

10. An arrangement for operating electronic control circuits including a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode, comprising means for applying an alternatin operating voltage to said anode and said cathode, and starting circuit means including transformer means and a variable detecting impedance for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, said transformer means being so constructed and arranged that the phase of the voltage applied from the transformer means to said electrode leads that applied from the source to said anode, and said detecting impedance when reduced to a predetermined value negatively increasing said starter electrode potential and causing said starting circuit means to carry current flowing from said cathode to said electrode in sufilcient quantity in the presence of said negatively increased potential to ionize gas in said tube sufficiently between said cathode and said electrode to cause the tube to become conductive with cur-- rent flowing from said anode to said cathode, said phase shift causing the tube to become conductive before the peak of the anode voltage is reached and hence providing increased periods of conductivity of the tube.

'11. An electronic control circuit comprising a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode; an alternating current source arranged for applying an operating voltage to the load circuit including said anode and said cathode; operator means in said load circuit; a first and a second detecting impedance; a first starting circuit connected for energization from said source and including said first detecting impedance; a second starting circuit including in series connection said second detecting impedance, said starter electrode and said cathode; and means for electrically coupling said starting circuits; said starting circuits being arranged for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, and, upon change of the value of one of said detecting impedances, for negatively increasing said starter electrode potential and causing said second starting circuit to carry current flowing from said cathode to said electrode and adapted to ionize gas in the tube sufiiciently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode.

12. An electronic control circuit comprising a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode; an alternating current source arranged for applying an operating voltage to the load circuit including said anode and said oath-- source;

ode; operator means in said load circui 8 fi and a second starter transformer; a first and a second detecting impedance; means for connecting the primary of said first transformer to said source; a first starting circuit including in series connection the secondary or said first transformer, said first detecting impedance, and the primary or said second transformer; ond starting circuit including in series connection the secondary or said second transformer, said second detecting impedance, said starter electrode and said cathode; said starting circuits being arranged for applying to said electrode a potential that is negative with respect to the poe tential of said cathode and which provides a current path through said electrode and said cathode, and, upon change of the value of one of said detecting impedances, for negatively increasing said starter electrode potential and causing said second starting circuit to carry current flowing from said cathode to said electrode and adapted to ionize gas in the tube sufiiciently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said cathode.

13. An electronic control circuit comprising a gaseous discharge tube with anode, cathode and starter electrode of the type wherein the starter electrode is normally used for effecting a starting discharge between said starter electrode and said cathode; an alternating current source arranged for applying an operating voltage to the load circuit including said anode and said cathode; operator means in said load circuit; a first and a second starter transformer; a first and a second detecting impedance; means for connecting the primary of said first transformer to said source; a first starting circuit including in series connection the secondary of said first transformer, a limiting resistor, said first detecting impedance, a capacitor and the primary of said second transformer; a second starting circuit including in series connection the secondary of said second transformer, a limiting resistor, said second detecting impedance, said starter electrode and said cathode; and a capacitor bridging the gap between said electrode and said cathode; said starting circuits being arranged for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, and, upon change of the value of one of said detecting impedances, for negatively increasing said starter electrode potential and causing said second starting circuit to carry current flowing from said cathode to said electrode and adapted to ionize gas in the tube sufficiently between said cathode and said electrode to cause the tube to become conductive with current flowing from said anode to said'cathode.

14. An electronic circuit for controlling combustion equipment including fuel supply means for heating a body of material, comprising a gaseous discharge tube with anode, cathode and starter electrode; an alternating current source arranged for applying an operating voltage to the load circuit including said anode and said cathode; operator means in said load circuit adapted to control said fuel supply means; a first and a second starter transformer; a phototube arranged for supervising the combustion of said fuel; probe impedance means for supervising the condition of said material; means for connecting the primary of said first transformer to said a first starting circuit including in series and a secconnection the secondary of said first transformer, a limiting resistor, said probe impedance means, a quantity of said material, and the primary of said second transformer; and a second starting circuit including in series connection the secondary of said second transformer, a limiting resistor, said phototube, said starter electrode and said cathode; said starting circuits being arranged for applying to said electrode a potential that is negative with respect to the potential of said cathode and which provides a current path through said electrode and said cathode, and, ,upon change of the conductivity of said photo tube or said probe means, for negatively increasing said starter electrode potential and causing said second starting circuit to carry current flowing from said cathode to said electrode, whereby said tube is rendered conductive to energize said fuel supply means, and said fuel supply means is controlled by the condition of either said combustion or said material.

PHILLIP J. CADE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,996,556 Sinden Apr. 2, 1935 2,071,958 Watrous Feb, 23, 1937 2,317,783 Lewis Apr. 27, 1943 2,358,432 Wolfner, 2nd Sept. 19, 1944 2,020,917 Stogofl Nov. 12, 1935 2,352,240 Woliner, 2nd June 27, 1944 

